The instant invention relates generally to lost wax investment casting, and more specifically to apparatus for removing investment material from an investment casting.
The lost wax investment casting process is used in the molding of high temperature metals that cannot be molded in rubber. In casting by the lost wax process preliminary patterns of the parts to be cast are formed by any suitable means, such as rubber molds, from a meltable material such as wax or the like. For example, the wax materials may be introduced into a rubber mold having the desired pattern cavities under high temperature and pressure to produce the desired wax patterns, and thereafter the wax is allowed to cool. After cooling, the wax patterns are removed from the mold and attached to a wax trunk or rod by their runners or gates, thereby forming a tree-shaped wax model. The wax tree model is placed on a circular rubber base and a cylindrical metal flask is then slid over the base. The wax tree is then embedded in a gypsum-based investment material which comprises a gypsum-based powder mixed with water. More specifically, the investment material is mixed, evacuated to remove air pockets, and then poured into the top of the cylinder completely embedding the wax tree therein, and thereafter the investment is allowed to solidify. After the investment solidifies, the wax is removed from the investment flask mold by placing the flask in an oven where the wax is melted and burnt out, leaving the investment flask mold with the desired pattern cavities therein. Casting metal is then introduced into the mold by vacuum or centrifugal techniques, and thereafter, the metal is allowed to harden.
After the metal is hardened, the investment material must be removed from the cylindrical flask and separated from the cast metal tree and parts. Heretofore, investment removal has primarily been accomplished by high pressure water blasting in which high pressure air and water are applied to the ends of an investment flask which is maintained at an elevated temperature. The high pressure of the water and air function to blast away the investment material from the cast parts, and the elevated temperature of the flask creates a steam effect when the water is introduced, thus helping to disintegrate the investment. The cast parts are thereafter sandblasted to remove any remaining investment material after which conventional final finishing operations are employed. Although the water blasting method has proven to be generally satisfactory, the introduction of water to the investment material causes several disposal problems which are readily apparent. The introduction of water to the investment material increases the weight of the waste investment and thus increases disposal costs. In order to dispose of the saturated investment material the investment must be separated from the water in settling tanks, and this alone is a lengthy and difficult process. In addition, the investment material may contain trace elements of toxic metal from the casting process, and in turn, waste water from the settling process may contain traces of investment material. Therefore, both the investment material and the waste water must be appropriately disposed of so as to not create environmental concerns.
Investment removal has also been accomplished using dry processes in which the investment mold is pushed out of the flask and then manually pounded to break away and separate the investment material from the cast metal parts. Several problems are readily apparent in the above-described procedure. Manually separating the cast parts is labor intensive and introduces a high degree of risk of damaging the cast parts. In addition, there is also a high percentage of investment left on the parts after manual separation, and thus the parts require more sandblasting than with the wet process. For all of the foregoing reasons, the existing investment removal techniques have been found to be inadequate.